Occasional erratic bursts southward of the East Australian Current (EAC) are thought to have moderated the weather of south-east Australia this autumn and winter and they continue to introduce tropical and sub-tropical marine species to Tasmanian waters.

Had our little friend Nemo the clownfish been riding the EAC this year he might have found himself holidaying in Tasmania rather than admiring the Sydney Opera House. He wouldn’t have been on the trip alone, though. Sea nettles (Chrysaora) have headed from their usual home in Sydney to be found for the first time ever in Tasmania and the Gippsland Lakes.

Chrysaora woodbridge, or sea nettle, was found in surprising numbers in Tasmania this year. Lisa-ann Gershwin, Author provided

Waters in the EAC travel southward along the east coast of Australia, with most of it splitting from the coast near Sydney and heading for New Zealand. A small part of the current, known as the EAC Extension, works its way southward past Victoria and Tasmania.

A typical signature in this region are the large eddies, around 200 kilometres across and hundreds of metres deep. Some of the warm water is trapped here along with marine life.

The EAC starts at the Great Barrier Reef and travels south to Sydney before turning eastward to New Zealand. Some of the water can still push southward via a series of strong eddies.Eric Oliver

This year a larger proportion of the EAC was sent southward instead of breaking away to the east. Winter ocean temperatures off Bass Strait were around 19C, an increase of 4C. This impacted local fishing, beach conditions and the weather.

In the video (above) the animation on the left shows the actual sea surface temperature and speed of the ocean currents. The animation on the right shows the difference in the temperature from average conditions.

Through autumn and winter, you can see two interesting changes occur. A strong warm current heads down the coast from Sydney to the coast of Victoria. At the same time, warm water peels off from the EAC and swirls around in large eddies as it meanders toward Tasmania.

An unusual catch down south

One advantage of warm eddies is the refuge they provide for tuna. They congregate in the centre of the eddy where the waters are warm and dine at the nutrient-rich edges.

Local fishers in north-east Tasmania report a remarkable year that allowed them to fish longer than usual, providing game fishers with more opportunities to catch tuna.

Last summer’s (2013-2014) warmth provided an abundance of skipjack and striped marlin, while winter brought a run of bluefin tuna.

Redmap is a website where locals can report sightings of marine species that are unusual for a given area.

Last summer a manta ray, a tropical cartilaginous fish (in a group including rays and skates), was sighted off the north-eastern coast of Tasmania. Previously the southern-most sighting of a manta ray was just south of Sydney.

Its not just new species visiting Tassie either. Local jellyfish such as the Lion’s Mane (cyanea) – more commonly known as “snotty” – are usually quite elusive, but turned up in unprecedented numbers last summer in Tasmania.

But there’s a catch

This movement south of the EAC may have an impact on other systems, including our health. We rely on fish such as those from the Tasman Sea as a source of omega-3 fatty acids for our brain health. But the concentration of omega-3 fatty acids in the fish is likely to decrease with global warming.

The original source of fatty acids come from algal species. As our waters warm, we will see more of the algae from the tropics take up residence in the south-east.

But the algae from the tropics are much smaller, which means more steps in the food chain from the algae to the fish we eat. The more steps in the food chain, the more the omega-3 fatty acids in the fish are replaced by fatty acids that are less favourable to brain health.

The warmer coastal waters also contributed to the balmy autumn and winter in south-eastern Australia this year. Afternoon sea breezes cool coastal temperatures by drawing cool oceanic air onto the coast.

Sydney’s heat wave in May this year had 19 consecutive days of 22C or more – this is partly due to the sea breezes failing to bring in the usual cooling air.

What’s causing the EAC to move south?

Over the past 50 years the EAC Extension has stretched about 350km further south. This extension doesn’t happen smoothly but in erratic bursts.

The southward extent of the EAC is controlled by the collective behaviour of the winds between Australia and South America. Over that same 50-year period these winds changed their pattern due to a strengthening of a climate system known as the Southern Annular Mode.

The changes to this mode have been attributed to a combination of ozone depletion and increasing atmospheric CO2.

The bushfire season isn’t wasting any time this year. There are already large fires in South Australia and NSW, and the obligatory ‘the state is a tinderbox’ warnings came out months ago. There were bushfires in July in NSW, and the number of local council areas in southern Australia declaring the fire season open in August – it starts in July up north – has more than doubled.

So a program on SBS on bushfires is timely. Inside the Inferno screens at 8.30pm on 5 November and 12 November. It’s mainly about the everyday heroes who volunteer to fight bushfires. But there’s a fair bit about the science of bushfires, and that’s where we come in. We contributed to the program, but much more importantly, we contribute to helping keep people safe from fires.

You might be surprised at how much of our work has a connection to fires. It’s not all we work on, obviously, but many areas of science go into prediction and management of fire.

And you need to know exactly what you’re planning for. That’s what the Pyrotron helps us do. It’s a 25 metre long fire-proof wind tunnel, with a working section for conducting experiments and a glass observation area.

It’s used to study – safely, under controlled conditions – how fires ignite in bushfire fuel and how they spread. Obviously, this is necessary work that can’t be done in the field under wildfire conditions. Using the Pyrotron we can study the mechanisms of bushfires’ spread, their thermokinetics – the chemistry of combustion – and fuel consumption, emissions and residues under different burning conditions.

But we won’t ever be able to prevent fires breaking out. We can plan, we can study, but we can’t change the nature of Australia. We can’t stop hot, dry days or lightning strikes. What we can do is find the safest way to live in our combustible climate.

Fire is one of many influences that define our living space. The challenge is to find acceptable ways of living with bushfires while retaining the ability to choose where and how we live. We also need to dispel some of the myths about bushfires that have put people and property in greater danger than was necessary. And we need to understand the risks from bushfires inherent in different types of construction. We need to know what’s safest and strongest, and how to build it.

We’ve surveyed every bushfire involving significant house loss since the 1983 Ash Wednesday fires, and we’ve tested a variety of construction methods to find optimal building types for fire-prone areas. How do we test them? The obvious – only – way. We set fire to them.

It’s not just how resistant they are to collapsing into a pile of ashes that’s important, although obviously that’s a major consideration. We also need to know what kind of house would best enable people to shelter in them while actively defending them from the bushfire attack. To put this all together, we use our expertise in:

It’s a lot, but we don’t stop there. We also work on disaster management tools for fires. We developed the Emergency Response Intelligence Capability (ERIC) in collaboration with the Australian Government Department of Human Services Emergency Management team.

This uses information from a range of sources and includes:

region data from the Australian Bureau of Statistics

context data including demographics and details of the natural and built environment

‘live’ data feeds describing the emergency event as it progresses and the historical record of previous ‘live’ data feeds

an archive of previous situation reports

This information can be focused for a specific region under investigation and collated semi-automatically to generate situation reports. The situation reports include information synthesised from available datasets and augmented by user provided content. The situation reports it generates describe what the event is, where it is located and the impact on the local community and to the department.

These days, social media is one of the most important channels when a disaster is unfolding, so we’re working on that too. Every minute, vast amounts of information are communicated via Twitter. Our challenge is to make relevant information accessible to emergency services.

Without suitable tools this information can’t be used. A huge amount of detail about the 2009 Victorian bushfires was reported in real-time on social network sites. The trouble was that state and federal disaster response agencies couldn’t see it.

We’ve created Emergency Situation Awareness (ESA) software to detect unusual behaviour in the Twittersphere and alert users in the emergency services if a disaster is unfolding online.

So that’s our contribution to helping keep people safe from bushfires, and, if worst comes to worst, in them. We hope it helps the firies – they deserve all the help they can get.

As heads of state gather in New York for tomorrow’s United Nations climate summit, a new report on the state of the world’s carbon budget tells them that greenhouse emissions hit a new record last year, and are still growing.

It shows that global emissions from burning fossil fuels and cement production reached a new record of 36 billion tonnes of CO2 in 2013, and are predicted to grow by a further 2.5% in 2014, bringing the total CO2 emissions from all sources to more than 40 billion tonnes. This is about 65% more fossil-fuel emission than in 1990, when international negotiations to reduce emissions to address climate change began.

Meanwhile, deforestation now accounts for just 8% of total emissions, a fraction that has been declining for several decades.

The growth of global emissions since 2009 has been slower than in the prior period of 2000-08. However, projections based on forecast growth in global gross domestic product (GDP) and continuance of improving trends in carbon intensity (emissions per unit of GDP) suggest a continuation of rapid emissions growth over the coming five years.

Global emissions continue to track the most carbon-intensive range among more than a thousand scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). If continued, this situation would lead to global average temperatures between 3.2C and 5.4C above pre-industrial levels by 2100.

There have been other striking changes in emissions profiles since climate negotiations began. In 1990, about two-thirds of CO2 emissions came from developed countries including the United States, Japan, Russia and the European Union (EU) nations. Today, only one-third of world emissions are from these countries; the rest come from the emerging economies and less-developed countries that account for 80% of the global population, suggesting a large potential further emissions growth.

Continuation of current trends over the next five years alone will lead to a new world order on greenhouse gas emissions, with China emitting as much as the United States, Europe and India together.

Country emission profiles

There are several ways to explore countries’ respective contributions to climate change. These include current emissions, per capita emissions, and cumulative emissions since the industrial revolution.

Carbon dioxide emissions from the combustion of fossil fuels and cement production for five regions. Cumulative emissions, production emissions (emissions generated in the region where goods and services are produced), consumption emissions (emissions generated in the region where goods and services are consumed), population, and GDP. 2012 is the most recent year for which all data are available.CDIAC, Global Carbon Project 2014

The largest emitters in 2013 were China, the United States, the 28 EU countries (considered as a single bloc), and India. Together, they account for 58% of global emissions and 80% of the emissions growth in 2013 (with the majority the growth coming from China, whereas the EU cut its emissions overall).

Here’s how the major emitters fared in 2013.

China

Emissions grew at 4.2%, the lowest level since the 2008 global financial crisis, because of weaker economic growth and improvements in the carbon intensity of the economy. Per capita emissions in China (7.2 tonnes of CO2 per person) overtook those in Europe (6.8 tonnes per person).

A large part of China’s high per capita emissions is due to industries that provide services and products to the developed world, not for China’s domestic use. China’s cumulative emissions are still only 11% of the total since pre-industrial times.

United States

Emissions increased by 2.9% because of a rebound in coal consumption, reversing a declining trend in emissions since 2008. Emissions are projected to remain steady until 2019 in the absence of more stringent climate policies, with improvements in the energy and carbon intensity of the economy being offset by growth in GDP and population. The United States remains the biggest contributor of cumulative emissions with 26% of the total.

European Union

Emissions fell by 1.8% on the back of a weak economy, although reductions in some countries were offset by a return to coal led by Poland, Germany and Finland. However, the long-term decrease in EU emissions does not factor in the emissions linked to imported goods and services. When accounting for these “consumption” emissions, EU emissions have merely stabilised, rather than decreased.

India

Emissions grew by 5.1%, driven by robust economic growth and an increase in the carbon intensity of the economy. Per capita emissions were still well below the global average, at 1.9 tonnes of CO2 per person, although India’s total emissions are projected to overtake those in the EU by 2019 (albeit for a population nearly three times as large). Cumulative emissions account for only 3% of the total.

Australia

Emissions from fossil fuels declined in 2013, largely driven by a 5% decline of emissions in the electricity sector over the previous year (as shown by the Australian National Greenhouse Gas Accounts). Fossil fuel emissions per person remain high at 14.6 tonnes of CO2.

Is it too late to tame the climate?

Our estimates (see here and here) show that, at current emissions levels, average global warming will hit 2C in about 30 years.

Despite this apparently imminent event, economic models can still come up with scenarios in which global warming is kept within 2C by 2100, while both population and per capita wealth continue to grow. Are these models playing tricks on us?

Most models invoke two things that will be crucial to stabilising the climate at safer levels. The first is immediate global action to develop carbon markets, with prices rapidly growing to over US$100 per tonne of CO2.

The second is the deployment of “negative emissions” technologies during the second half of this century, which will be needed to mop up the overshoot of emissions between now and mid-century. This will involve removing CO2 from the atmosphere and storing it in safe places such as saline aquifers.

These technologies are largely unavailable at present. The most likely candidate is the production of bioenergy with carbon capture and storage, a combination of existing technologies with high costs and with environmental and socio-economic implications that are untested at the required scales.

There are no easy pathways to climate stabilization, and certainly no magic bullets. It is still open to us to choose whether we halt our CO2 emissions completely this century – as required for a safe, stable climate – or try instead to adapt to significantly greater impacts of climate change.

What we have no choice about is the fact that the longer emissions continue to grow at rates of 2% per year or more, the harder it will be to tame our climate.

Pep Canadell received support from the Australian Climate Change Science Program.

Michael Raupach has previously received funding from the Australian Climate Change Science Program, but does not do so now.

There is less than 1 chance in 100,000 that global average temperature over the past 60 years would have been as high without human-caused greenhouse gas emissions, our new research shows.

Published in the journal Climate Risk Management today, our research is the first to quantify the probability of historical changes in global temperatures and examines the links to greenhouse gas emissions using rigorous statistical techniques.

Our new CSIRO work provides an objective assessment linking global temperature increases to human activity, which points to a close to certain probability exceeding 99.999%.

It is extremely likely [defined as 95-100% certainty] that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic [human-caused] increase in greenhouse gas concentrations and other anthropogenic forcings together.

Decades of extraordinary temperatures

July 2014 was the 353rd consecutive month in which global land and ocean average surface temperature exceeded the 20th-century monthly average. The last time the global average surface temperature fell below that 20th-century monthly average was in February 1985, as reported by the US-based National Climate Data Center.

This means that anyone born after February 1985 has not lived a single month where the global temperature was below the long-term average for that month.

We developed a statistical model that related global temperature to various well-known drivers of temperature variation, including El Niño, solar radiation, volcanic aerosols and greenhouse gas concentrations. We tested it to make sure it worked on the historical record and then re-ran it with and without the human influence of greenhouse gas emissions.

Our analysis showed that the probability of getting the same run of warmer-than-average months without the human influence was less than 1 chance in 100,000.

We do not use physical models of Earth’s climate, but observational data and rigorous statistical analysis, which has the advantage that it provides independent validation of the results.

Detecting and measuring human influence

Our research team also explored the chance of relatively short periods of declining global temperature. We found that rather than being an indicator that global warming is not occurring, the observed number of cooling periods in the past 60 years strongly reinforces the case for human influence.

We identified periods of declining temperature by using a moving 10-year window (1950 to 1959, 1951 to 1960, 1952 to 1961, etc.) through the entire 60-year record. We identified 11 such short time periods where global temperatures declined.

Our analysis showed that in the absence of human-caused greenhouse gas emissions, there would have been more than twice as many periods of short-term cooling than are found in the observed data.

There was less than 1 chance in 100,000 of observing 11 or fewer such events without the effects of human greenhouse gas emissions.

Good risk management is all about identifying the most likely causes of a problem, and then acting to reduce those risks. Some of the projected impacts of climate change can be avoided, reduced or delayed by effective reduction in global net greenhouse gas emissions and by effective adaptation to the changing climate.

Ignoring the problem is no longer an option. If we are thinking about action to respond to climate change or doing nothing, with a probability exceeding 99.999% that the warming we are seeing is human-induced, we certainly shouldn’t be taking the chance of doing nothing.

The authors do not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article. They also have no relevant affiliations.

Here’s a simple backyard science experiment for you to try, which has global implications.

Grab a garden hose, turn it on, and then put your thumb over the end of it. The flow of water thins, while its power intensifies.

Okay, now multiply that by a few million and you have some idea of the impact of recent La Niña conditions on a major ocean current north of Australia.

The Indonesian Throughflow is a series of ocean currents linking the Pacific and Indian Oceans. It carries water from the Pacific to the Indian Ocean through the passages and straits of the Indonesian Archipelago.

Schematic of the ITF. Values of the flow and the major passages are indicated by red. Water enters the ITF from the western Pacific and exits into the Indian Ocean. Image: Wikipedia.

Researchers – led by Janet Sprintall at Scripps Institution of Oceanography in the United States, and including Susan Wijffels from CSIRO in Hobart – have found that the flow of water in the Indonesian Throughflow has become more shallow and intense since the late 2000s due to La Niña conditions, just as the water flow thinned and intensified while you played with that garden hose.

The Indonesian Throughflow is the only place in the world where warm equatorial waters flow from one ocean to another; consequently, the throughflow is an important chokepoint in the flow of heat in the climate system.

The paper suggests that human-caused climate change could make this shallowing and intensification a more dominant feature of the Indonesian Throughflow, even under El Niño conditions.

Changes in how much warm water is carried by the Indonesian Throughflow will affect the sea surface temperature, and in turn the patterns of rainfall in our region.

So you may need to think a bit more about how you use that garden hose.

We wait in anticipation of droughts and floods when El Niño and La Niña are forecast but what are these climatic events?

The simplest way to understand El Niño and La Niña is through the sloshing around of warm water in the ocean.

The top layer of the tropical Pacific Ocean (about the first 200 metres) is warm, with water temperatures between 20C and 30C. Underneath, the ocean is colder and far more static. Between these two water masses there is a sharp temperature change known as the thermocline.

Winds over the tropical Pacific, known as the trade winds, blow from east to west piling the warm top layer water against the east coast of Australia and Indonesia. Indeed, the sea level near Australia can be one metre higher than at South America.

Warm water and converging winds near Australia contribute to convection, and hence rainfall for eastern Australia.

La Niña. Image: US National Weather Service

In a La Niña event, the trade winds strengthen bringing more warm water to Australia and increasing our rainfall totals.

El Niño. Image: US National Weather Service

In an El Niño the trade winds weaken, so some of the warm water flows back toward the east towards the Americas. The relocating warm water takes some of the rainfall with it which is why on average Australia will have a dry year.

In the Americas El Niño means increased rainfall, but it reduces the abundance of marine life. Typically the water in the eastern Pacific is cool but high in nutrients that flow up from the deep ocean. The warm waters that return with El Niño smother this upwelling.

Have El Niño and La Niña always been around?

El Niño and La Niña are a natural climate cycle. Records of El Niño and La Niña go back millions of years with evidence found in ice cores, deep sea cores, coral and tree rings.

El Niño events were first recognised by Peruvian fisherman in the 19th century who noticed that warm water would sometimes arrive off the coast of South America around Christmas time.

Because of the timing they called this phenomenon El Niño, meaning “boy child”, after Jesus. La Niña, being the opposite, is the “girl child”.

Predicting El Niño and La Niña

Being able to predict an El Niño event is a multi-million, possibly billion dollar question.

Reliably predicting an impending drought would allow for primary industries to take drought protective action and Australia to prepare for increased risk of dry, hot conditions and associated bushfires.

Unfortunately each autumn we hit a “predictability barrier” which hinders our ability to predict if an El Niño might occur.

In autumn the Pacific Ocean can sit in a state ready for an El Niño to occur, but there is no guarantee it will kick it off that year, or even the next.

Nearly all El Niños are followed by a La Niña though, so we can have much more confidence in understanding the occurrence of these wet events.

A variety of events

Predictability would be even easier if all El Niños and La Niñas were the same, but of course they are not.

Not only are the events different in the way they manifest in the ocean, but they also differ in the way they affect rainfall over Australia – and it’s not straightforward.

The exceptionally strong El Niños of 1997 and 1982 have now been termed Super El Niños. In these events the trade winds weaken dramatically with the warm surface water heading right back over to South America.

Recently a new type of El Niño has been recognised and is becoming more frequent.

This new type of El Niño is often called an “El Niño Modoki” – Modoki being Japanese for “similar, but different”.

In these events the warm water that is usually piled up near Australia heads eastward but only makes it as far as the central Pacific. El Niño Modoki occurred in 2002, 2004 and 2009.

Australian rainfall is affected by all its surrounding oceans. El Niño in the Pacific is only one factor.

As a general rule though, the average rainfall in eastern and southern Australia will be lower in an El Niño year and higher in a La Niña. The regions that will experience these changes and the strength are harder to pinpoint.

El Niño and climate change

It is not yet clear how climate change will affect El Niño and La Niña. The events may get stronger, they may get weaker or they may change their behaviour in different ways.

Some research is suggesting that Super El Niños might become more frequent with climate change, while others are hypothesising that the recent increase in El Niño Modoki is due to climate change effects already having an impact.

Because climate change in general may decrease rainfall over southern Australia and increase potential evaporation (due to higher temperatures) then it would be reasonable to expect that the drought induced by El Niño events will be exacerbated by climate change.

Given that we are locked into at least a few degrees of warming over the coming century, it’s hard not to fear more drought and bushfires for Australia.

Record-breaking rains triggered so much new growth across Australia that the continent turned into a giant green carbon sink to rival tropical rainforests including the Amazon, our new research shows.

Published in the international journal Nature, our study found that vegetation worldwide soaked up 4.1 billion tons of carbon in 2011 – the equivalent of more than 40% of emissions from burning fossil fuels that year.

Unexpectedly, the largest carbon uptake occurred in the semi-arid landscapes of Australia, Southern Africa and South America.

The modelled net carbon uptake of the Australian landscape in December 2010 at the start of the big wet (top), compared with December 2009 (bottom).

It set a new record for a land-based carbon sink since high-resolution records began in 1958, in a remarkable example of ecosystems working to stabilise the Earth’s climate.

And that had a global impact. While atmospheric carbon dioxide still rose in 2011, it grew at a much lower rate – nearly 20% lower – than the average growth over the previous decade.

Almost 60% of the higher than normal carbon uptake that year, or 840 million tons, happened in Australia. That was due to a combination of factors, including geography and a run of very dry years, followed by record-breaking rains in 2010 and 2011.

Yet our research raises as many questions as it answers – in particular, about whether the Earth’s natural climate control mechanisms could prove even more volatile than previously thought.

Averaged across Australia, the Bureau of Meteorology recorded rainfall of 703 millimetres for 2010 and 708 mm for 2011. That was well above the long-term average of 453 mm for the period of 1900 to 2009.

The big rainfall event was part of a global phenomenon called the El Niño Southern Oscillation (ENSO), which reflects atmospheric pressure changes across the tropical Pacific Ocean, in its La Niña phase. It brought above-average rainfall not only to Australia but also to other parts of the world, particularly in southern Africa and northern South America.

The power of La Niña to evaporate water from the oceans was boosted by the ongoing high sea-surface temperatures that are part of a long-term trend of ocean warming. That trend has been shown to be associated with the release of greenhouse gases from the combustion of fossil fuels and deforestation.

This massive rain event was so significant that sensors on-board the twin satellites GRACE estimated a decrease in ocean water mass of 1.8 trillion tons. That remarkable finding was measured by changes in the Earth’s gravitational field, brought about by the transfer of water from the ocean to the atmosphere and land surface.

The drop in global sea level in 2011, which went against the trend of the previous 18 years. Image: Boening et. al. (2012), CC BY

Australia played a major role in this sea-level fall, for several reasons. It was partly due to vast amounts of rain that fell over Australia. The continent’s hydrological characteristics also played a role, with large impediments for rainfall to flow quickly back to the ocean, such as the large continental interior basins.

And Australia was a country in need of a big drink. The parched continent was emerging from a multi-year drought, particularly in the south-east region, meaning the land acted as a huge sponge, soaking up the heavy rainfall.

Seeing the Earth change colour from above

As a result of the unusually heavy rains, the Earth’s vegetation “greened” in 2011 in ways not measured over the previous 30 years, particularly in the Southern Hemisphere dryland ecosystems.

This global greening was detected by satellites, which observed increases in canopy foliage extent and vegetation water content, which both imply vegetation growth.

Combined, these measurements indicated that the world’s annual production of new plant matter significantly increased in 2011 when compared to the previous decade.

Regions in the Southern Hemisphere including Australia, southern Africa, and temperate South America contributed 80% of the change, especially their savannas and other semi-arid areas.

New growth springing up around the Murray River, Hume Reservoir and Lake Tyrrell in south-eastern Australia, September 2010. Image: NASA, CC BY-NC-ND

That winter, June to August 2011, Australia was the greenest that it has ever been seen in the satellite period (since 1982).

The same region in September 2006. This and the image above show how growing conditions compared to average mid-September conditions over 2000 to 2011. See more images here: http://1.usa.gov/RSMka6 Image: NASA, CC BY-NC-ND

Our new study in Nature also shows how fire emissions – normally a big factor in reducing Australia’s capacity to store carbon – were suppressed by about 30%, contributing even further to the continent’s greening.

In addition to the unprecedented vegetation greening of Australia during 2010 and 2011, we also observe a greening trend over the continent since 1980s, particularly during the months of the Australian autumn (March, April, and May).

That has happened for a number of reasons, including increased continental rainfall over the past few decades; plants growing in an atmosphere with increasing carbon dioxide using water more efficiently; and changes in land management such as fire suppression, expansion of invasive species, and changes in livestock grazing that have led to more woodland.

The upsides of going green

Despite recurrent drought conditions in some regions, there is a current greening trend over Australia.

Overall, satellites show Australian landscapes are greener now than they have been over the past 30 years.

A greener Australia has a number of environmental and other benefits, including better protection for soils, increased soil-water holding capacity and soil fertility, and more plant feed to sustain larger animal populations.

However, more vegetation can lead to less water being available to replenish water tables and feed rivers, even though Australia loses more than 50% of all the rainfall to the atmosphere as soil evaporation, without contributing to vegetation growth.

This is in sharp contrast to temperate and tropical ecosystems, where a large part of the water is returned to the atmosphere via vegetation.

Fire, drought and rapid carbon release

However, we now need to consider whether this growing accumulation of carbon in semi-arid regions of the Southern Hemisphere could become a future climate liability through fire and drought.

Land and ocean carbon sinks absorb around half of the world’s emissions from burning fossil fuels each year, which helps to slow the rise of atmospheric carbon dioxide concentrations from human activities.

That’s a vital trend to consider, because it could lead to a more vulnerable global carbon reservoir.

While we might see more carbon stored in new vegetation growth and soil when extra water is available in semi-arid regions, as happened in 2010-2011, the risk is that more fires and droughts would end up rapidly releasing that carbon back to the atmosphere.

Looking ahead

It is likely that the large carbon uptake during 2011 was short-lived, as suggested by a rapid decline of the sink strength in 2012. Future research will be able to confirm if this was the case.

Arid and semi-arid regions currently occupy 40% of the world’s land area. More work is urgently needed to research the best ways to manage these areas, and whether we can increase their soil and vegetation carbon stores as part of our climate mitigation efforts.

Increasingly, semi-arid regions are driving variability in how much carbon dioxide remains in the Earth’s atmosphere each year. And that has major implications for the long-term, including whether future climate change will slow down or accelerate further.